1. Field of the Invention
The present invention relates to a tool holder, and more particularly to a tool holder for an electric discharge machine and that can be rotated in a vertical axle.
2. Description of Related Art
With reference to FIG. 10, a conventional tool holder for an electric discharge machine (EDM) in accordance with the prior art comprises a body (80), a top base (81), a conical base (87), an electrode base (89) and an electrode collar (90). The body (80) is rotatably attached to the top base (81). Multiple adjusting screws (83) are screwed into the body (80) to adjust the body (80) relative to the top base (81) in a limited range. A conical cavity (85) is defined in the bottom of the body (80). The conical base (87) is rotatably attached to the bottom of the body (80) with a main shaft (871). A conical surface (88) is formed on the top of the conical base (87) and received in the conical cavity (85). Multiple horizontal adjusting screws (86) are inclinedly screwed into the body (80) and each has a free end abutting the conical surface (88) of the conical base (87). When the horizontal adjusting screws (86) are rotated, the conical base (87) will be pushed to rotate relative to the body (80) so as to adjust the horizontal level of the conical base (87). The electrode base (89) is securely attached to the bottom of the conical base (87) and has a notch (891) defined in one side of the electrode base (89). The electrode base (89) is connected to the positive electrode of the electric discharging device of the EDM. The electrode collar (90) is securely attached to the electrode base (89) with securing bolts (91,92). One of the securing bolts (92) faces and extends into the notch (891) in the electrode base (89). Consequently, a tool can be securely attached the notch (891) in the electrode base (89) by the electrode collar (90) and the securing bolt (92).
When the electric discharge machine is in operation, the positive electrode of the electric discharge device is connected to the tool through the electrode base (89) and the negative electrode of the electric discharge device is connected to a workpiece. When the tool approaches the work, the electric power will be discharged from the tool to the workpiece so as to erode the workpiece to form a hole, a recess or a cavity or the like therein.
However, although the body (80) can rotate relative to the top base (81) to adjusting the working position of the tool, the rotating range of the body (80) relative to the top base (81) is very small. The tool attached to the conventional tool holder cannot be moved in a large range. For example, if the work will be formed with two holes at the opposite ends of a diameter of a circle, the tool holder must be released, rotated and locked to align with a position for forming another hole after one hole has been formed. The horizontal level of the body (80), the conical base (87) and the tool must be readjusted. To form the work in a large range with the conventional tool holder is inconvenient.
To overcome the shortcomings, the present invention tends to provide a tool holder to mitigate or obviate the aforementioned problems.
The main objective of the invention is to provide a tool holder for an electric discharge machine and that can be adjusted conveniently. The tool holder has a top base, a securing collar, a positioning sleeve, an adjusting base, a rotating base, a conical base, an electrode base and an electrode collar. The top base is secured to a base of the electric discharge machine and has a central hole and an elongated opening communicating with the central hole. The securing collar is screwed into the central hole in the top base and has a central hole with a conical inner surface. Multiple holes are defined around the securing collar and correspond to the elongated opening in the top base. A positioning sleeve is received in the central hole of the securing collar and has a conical outer surface fitting with the conical inner surface in the securing collar. The adjusting base is rotatably attached to the bottom of the top base and has a main shaft penetrating through the central hole in the positioning sleeve and into the central hole in the top base. The rotating base is adjustably connected to the bottom of the middle base and for the conical base, electrode base and the electrode collar being connected to the bottom of the rotating base. In such an arrangement, the locked condition of the main shaft is released by means of the rotating the securing collar, such that the adjusting base with the rotating base can be rotated relative to the top base. Consequently, a tool attached to the electrode base can be moved to a position at a circle conveniently.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.